1. Field of the Invention
The invention relates to a combined front-end circuit for a communication terminal device with multi-band and/or multi-mode transmission system.
2. Description of the Related Art
The numerous, existing wireless transmission systems, particularly mobile radiotelephone systems, can differ both with respect to the transmission standard as well as with respect to the frequency bands employed. Different access methods are also employed, for example, CDMA (Code Division Multiple Access), TDMA (Time Division Multiple Access) or FDMA (Frequency Division Multiple Access).
These different access methods can also comprise different duplex methods in order to separate the transmission and reception data and enable a simultaneous transmission and reception mode at the communication terminal device. FDD (Frequency Division Duplex) and TDD (Time Division Duplex) are known as duplex methods. Some standards also use a duplex method with mixed FDD/TDD mode in which different frequency bands are used for the transmission and reception mode, but the transmission and reception signals are additionally separated from one another in time and are arranged in “time slots”. Known transmission standards in the USA are, for example, CDMA 800 and CDMA 1900, whose duplex method ensues in a pure FDD mode. The GSM standard with the individual bands GSM 1800, GSM 1900 and EGSM, whose duplex method ensues in mixed FDD/TDD mode, is widespread in Europe. The TDMA 800 and TDMA 1900 standards encountered in the USA likewise comprise a mixed FDD/TDD mode. In addition, the analog AMPS standard, which works with a pure FDD mode, is also widespread in the USA.
Simple mobile radiotelephone devices (cell phones) make use of a single standard and are therefore only suited for unlimited operation in the regions in which an adequate coverage for this standard is established. Multi-band mobile radiotelephone devices that can cover a plurality of frequency bands are suited for better reachability in regions with incomplete network coverage or for increasing capacity in regions with many users. “Dual-band” and “triple-band” cell phones function according to the same access method (for example, GSM), but can transmit and receive in different frequency bands and are therefore equipped for a plurality of standards, for example, simultaneously for GSM 1800 and EGSM or, additionally, for GSM 1900 as well. Corresponding multi-band cell phones exist for the US market, particularly for the CDMA systems at 800 and 1900 MHz.
In known multi-band mobile radiotelephone terminal devices for standards with a mixed FDD/TDD duplex mode, the access onto the common antenna for transmission (Tx) and reception (Rx) is usually realized via an RF switchover. One transmission system thereby respectively utilizes one (frequency) band pair in which the frequencies for transmission and reception are arranged. When a band pair of a system is at an adequately great distance from the other bands (typically about 1 octave), then the filters and the signal processing paths for this band pair, separated from the others, can be interconnected and connected to the common antenna in an impedance-neutral fashion via a diplexer. The band pairs of other standards that lie closer to one another are usually separated from one another via a multiple switch in known multi-band terminal devices.
FIG. 1 shows a front-end circuit of a known triple band GSM system. The circuit is suited for communication terminal devices (for example, cell phones) that can work in three different GSM bands, namely GSM 1800, GSM 1900 and EGSM. In terms of frequency, the transmission and reception band for the EGSM system is clearly separated from the band pairs for the two other GSM systems and is at a distance of above 1 octave. A separation of these two band ranges ensues with a diplexer DI1 (i.e., a passive frequency separating filter) that is composed of a high pass filter HDI1 and of a low pass filter LDI1 that are interconnected in parallel with the antenna A. A switchover US1 that optionally connects the output of the low pass filter LDI1 to the transmission filter SF3 or to the reception filter EF3 of the EGSM system is arranged at the output of the low pass filter. The other output TX3 of the transmission filter, which is fashioned as low pass filter, is connected to a power amplifier (PA) (not shown). Likewise, the other output RX3 of the reception filter EF3 is connected to a low noise amplifier (LNA) (not shown). The EGSM system with mixed FDD/TDD mode work time-offset for transmission and reception in different time slots by which the switchover US1 produces the connection to the corresponding filter and the signal processing path depending on the respective time slot.
The second output of the diplexer DI1 (i.e., the output of the high pass filter HDI1) is connected to a multiple switch MS1 that can switch back and forth between the transmission and reception filters of the two other GSM bands. For transmitting, a common low pass filter is used as a transmission filter SF1,2 for both bands. A respective, discrete band pass filter EF1 and EF2 is available for the reception via the two reception paths Rx1 and Rx2. Depending on the desired band, the multiple switch MS1 for transmission and reception switches back and forth between the two switch points 1 and 2 or 1 and 3.
System-overlapping mobile radiotelephone terminal devices that can use different access methods (“multi-mode devices”) have not yet been disclosed. Terminal devices for mobile radiotelephony of the third generation (3 G) that are set to be introduced in the next few years, are likewise not known.